1. Field of the Invention
The present invention relates to an image generating apparatus comprising a print head printing images while pressing a platen roller with prescribed pressing force.
2. Description of the Background Art
An image generating apparatus comprising a print head printing images while pressing a platen roller with prescribed pressing force and the like is known in general, as disclosed in each of Japanese Patent Nos. 3817732, 2756029 and 3177126, and Japanese Patent Laying-Open Nos. 2003-266859 and 6-39980 (1994), for example.
The aforementioned Japanese Patent No. 3817732 discloses a thermal transfer printer (image generating apparatus) comprising a cam gear, a driving gear, a shaft member (rotational member) having driving gear mounting portions and synchronous cam portions integrally provided on both ends of a rotating shaft respectively and a thermal head (print head) supported by an arm through a spring. In the thermal transfer printer (image generating apparatus) described in Japanese Patent No. 3817732, control bosses provided on the arm supporting the thermal head engage with notches formed on the driving gear mounting portions of the shaft member when the cam gear and the driving gear mounted on the shaft member through the driving gear mounting portions mesh with each other to rotate the shaft member by a prescribed angle, thereby regulating rotation of the thermal head.
The aforementioned Japanese Patent No. 2756029 discloses a printer driving mechanism comprising a swing gear driven by a drive motor, a swing plate mounted with a head-down gear and a head-up gear and swung by the swing gear, a cam gear and a head separating cam lever engaging with the cam gear. In the printer driving mechanism described in Japanese Patent No. 2756029, the head-down gear or the head-up gear selectively meshes with the cam gear due to an operation of the swing plate interlocking with the swing gear, for vertically rotating the print head through the head separating cam lever engaging with the cam gear. When the head-down gear engages with an intermittent portion (toothless portion) provided on the cam gear by meshing with the cam gear, rotation of the cam gear is stopped regardless of rotation of the swing gear driven by the drive motor.
The aforementioned Japanese Patent Laying-Open No. 2003-266859 discloses an ink jet recording apparatus (image generating apparatus) comprising a recording paper transportation motor and PG (paper gap) control means capable of vertically moving a carriage loaded with a recording head by successively meshing an endless belt, a plurality of transmission gears, a PG control gear and a swing portion with a pulley driven by the recording paper transportation motor. In the ink jet recording apparatus (image generating apparatus) described in Japanese Patent Laying-Open No. 2003-266859, the swing portion rotates by a prescribed angle for vertically moving a carriage guide shaft provided independently of the swing portion, thereby vertically rotating the carriage loaded with the recording head.
The aforementioned Japanese Patent No. 3177126 discloses a thermal printer (image generating apparatus) capable of reciprocating a carriage loaded with a thermal head in the cross direction of papers by successively meshing a carriage driving gear, a transmission gear and a roller driving gear with a stepping motor and an idle gear (intermediate gear) driven by the stepping motor. In the thermal printer (image generating apparatus) described in Japanese Patent No. 3177126, the carriage driving gear rotates by a prescribed angle, thereby moving the carriage loaded with the thermal head in the cross direction of the papers through a carriage driving shaft provided independently of the carriage driving gear.
The aforementioned Japanese Patent No. 6-39980 discloses a print head for a printer comprising a head motor, a driving gear rotated by the head motor and a head cam integrally provided with a gear portion meshing with the driving gear and a cam portion for applying pressing force to a pressing mechanism for a thermal head. In the print head for a printer described in Japanese Patent No. 6-39980, the driving gear rotates by a prescribed angle, thereby pressing the thermal head toward a platen through the head cam and the pressing mechanism. In the print head for a printer described in Japanese Patent No. 6-39980, the driving gear is in mesh with the gear portion of the head cam regardless of the operation of pressing the thermal head.
In the thermal transfer printer (image generating apparatus) described in the aforementioned Japanese Patent No. 3817732, however, rotation of the thermal head is regulated by the engagement between the control bosses of the thermal head and the notches of the driving gear mounting portions, whereby the engagement between the control bosses and the notches may conceivably be incomplete if the accuracy of the rotation angle of the cam gear is insufficient. In this case, constant pressing force cannot be obtained for the thermal head (print head). In the thermal transfer printer described in the aforementioned Japanese Patent No. 3817732, further, the driving gear is provided independently of the shaft member, whereby the number of components of the thermal transfer printer is disadvantageously increased.
In the printer driving mechanism described in the aforementioned Japanese Patent No. 2756029, the head-down gear is continuously rotated by the driving motor in the state engaging with the intermittent portion (toothless portion) of the cam gear when the print head presses the platen, whereby a toothed portion of the head-down gear may periodically come into contact with the intermittent portion of the cam gear, to vibrate the cam gear. If such vibration of the cam gear is propagated from the cam gear to the head separating cam lever, the head separating cam lever cannot apply constant pressing force to the print head due to jolting resulting from the vibration.
In the ink jet recording apparatus (image generating apparatus) described in the aforementioned Japanese Patent Laying-Open No. 2003-266859, the carriage guide shaft vertically moving the carriage is provided independently of the swing portion, whereby the number of components of the apparatus is disadvantageously increased.
Also in the thermal printer (image generating apparatus) described in the aforementioned Japanese Patent No. 3177126, the carriage driving shaft reciprocating the carriage is provided independently of the carriage driving gear, whereby the number of components of the thermal printer is disadvantageously increased.
In the print head for a printer described in the aforementioned Japanese Patent Laying-Open No. 6-39980 (1994), the driving gear is regularly in mesh with the gear portion of the head cam, whereby the rotation angle of the head cam is conceivably inconstant if the accuracy of the rotation angle of the driving gear is insufficient. In this case, constant pressing force cannot be obtained for the thermal head (print head).